The disclosure of Japanese Patent Application No. 2002-008313 filed on Jan. 17, 2002, including its specification, drawings, and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a vehicular steering device, a program, and a record medium. More particularly, the present invention relates to a vehicular steering device capable of changing a transfer ratio between a steering angle of a steering handle and a turning angle of a turning wheel, a program for causing a computer system to function so as to realize the vehicular steering device, and a computer-readable record medium in which the program is recorded.
2. Description of the Related Art
According to the art related to the present invention, various vehicular steering devices comprising a variable transfer-ratio unit for changing a transfer ratio between a steering angle of a steering handle and a turning angle of a turning wheel and an electric motor for driving the variable transfer-ratio unit have been proposed. These vehicular steering devices have a lock unit for stopping relative rotation of the electric motor.
The lock unit directly connects the steering handle and the turning wheel by stopping the relative rotation of the electric motor in the case of a failure in the electric motor or an electric motor driving circuit, or in some other cases.
The lock unit is composed of a stopper member for stopping relative rotation of the electric motor and a solenoid for driving the stopper member. If an electromagnetic coil constituting the solenoid is energized, the stopper member is driven and the electric motor is released.
In the lock unit of the related art, the electromagnetic coil constituting the solenoid is continuously energized without being interrupted while the electric motor is being released. Hence, the electromagnetic coil generates heat. If a long period is required to release the electric motor, the electromagnetic coil is sometimes heated up, for example, to a temperature of approximately 200xc2x0 C.
The vehicular steering devices of the related art have an operating angle sensor for detecting an operating angle of the electric motor. A transfer ratio between a steering angle of the steering handle and a turning angle of the turning wheel is set on the basis of the operating angle.
In the case where the operating angle sensor is embodied using a semiconductor device such as a Hall IC which exhibits a low heat resistance, if the temperature of the electromagnetic coil rises, there is an apprehension that heat generated therefrom will lead to a malfunction in the operating angle sensor or a reduction in life of the operating angle sensor.
Further, in the case where various semiconductor devices (e.g., an anti-noise capacitor and a non-return diode connected to a drive signal feed line leading to the electric motor, and the like) as well as the operating angle sensor are disposed close to the electromagnetic coil, if the temperature of the electromagnetic coil rises, there is an apprehension that heat generated therefrom will lead to a malfunction in the semiconductor devices or a reduction in life of the semiconductor devices.
The present invention has been made as a solution to the above-mentioned problems.
It is an object of the present invention to provide a vehicular steering device capable of suppressing heat generation.
It is another object of the present invention to provide a program for causing a computer system to function so as to realize the vehicular steering device.
It is still another object of the present invention to provide a computer-readable record medium in which a program for causing a computer system to function so as to realize the vehicular steering device is recorded.
A vehicular steering device in accordance with a first aspect of the present invention comprises a variable transfer-ratio unit for changing a transfer ratio between a steering angle of a steering handle and a turning angle of a turning wheel, an electric motor for driving the variable transfer-ratio unit, and a lock unit for switching between a locked state in which relative rotation of the electric motor is stopped and an unlocked state in which the electric motor is released. The lock unit comprises a stopper member for stopping relative rotation of the electric motor, an urging member for urging the stopper member such that the stopper member stops the electric motor, a solenoid for releasing the electric motor by driving the stopper member against an urging force of the urging member, and a control unit for controlling a voltage applied to the solenoid. After the electric motor has been released and has assumed the unlocked state, the control unit intermittently applies a voltage to the solenoid so as to maintain the electric motor in the unlocked state.
If a voltage is applied to the solenoid, a drive force is generated in the stopper member. If the drive force exceeds an urging force of the urging member, the electric motor is released and assumes the unlocked state. Accordingly, the drive force that is required for the maintenance of the electric motor in the unlocked state can be smaller than the drive force that is required for a shift of the electric motor from the locked state to the unlocked state.
Thus, as in the first aspect of the present invention, if a voltage is intermittently applied to the solenoid so as to maintain the electric motor in the unlocked state after the electric motor has been released and assumed the unlocked state, heat generation from the solenoid can be suppressed.
That is, heat that is generated while the voltage is applied to the solenoid is discharged while no voltage is applied to the solenoid. Therefore, heat generation can be suppressed more effectively in comparison with a case where a voltage is continuously applied to the solenoid as in the related art.
The vehicular steering device in accordance with the first aspect of the present invention may be structured such that, when switching from the locked state to the unlocked state, the control unit continuously applies a voltage to the solenoid until the electric motor is released.
Thus, according to the above-mentioned structure, the electric motor can be released without delay and brought into the unlocked state.
The vehicular steering device in accordance with the first aspect of the present invention may be structured such that the control unit changes, in coordination with a power-supply voltage applied to the solenoid, a duty ratio at which the voltage is intermittently applied to the solenoid.
If a voltage is applied to the solenoid, a drive force is generated in the stopper member. The drive force increases in proportion to an increase in the power-supply voltage, whereas the urging force of the urging member is constant. In order to maintain the electric motor in the unlocked state, it is appropriate that the drive force be equal to or larger than the urging force. Therefore, if the power-supply voltage is high, it is appropriate that the duty ratio at which the voltage is intermittently applied to the solenoid be set as a small value.
Thus, according to the above-mentioned structure, by performing duty control through application of the voltage to the solenoid at the duty ratio corresponding to the power-supply voltage, it becomes possible to prevent the drive force from becoming excessive in the case where the power-supply voltage is high, and to inhibit the solenoid from generating heat whose amount corresponds to an excess in the drive force.
The vehicular steering device in accordance with the first aspect of the present invention may be structured such that the control unit changes the duty ratio in a stepped manner in coordination with the power-supply voltage.
The vehicular steering device in accordance with the first aspect of the present invention may be structured such that, when the duty ratio is changed in the stepped manner, the control unit ensures that the duty ratio exhibits a hysteresis characteristic corresponding to the power-supply voltage.
If the solenoid causes the phenomenon of chattering during a change in application state of a voltage to the solenoid, the stopper member repeats its movements several times and then stabilizes. Thus, there is an apprehension that the electric motor will shift from the unlocked state to the locked state.
Thus, as in the above-mentioned structure, by ensuring that the duty ratio exhibits the hysteresis characteristic corresponding to the power-supply voltage, it becomes possible to prevent the solenoid from causing the phenomenon of chattering as a result of fluctuations in the power-supply voltage, and to stably maintain the electric motor in the unlocked state even during fluctuations in the power-supply voltage.
The vehicular steering device in accordance with the first aspect of the present invention may be structured such that the control unit continuously changes the duty ratio in coordination with the power-supply voltage.
The vehicular steering device in accordance with the aspect of the present invention may be structured such that the control unit linearly changes the duty ratio in coordination with the power-supply voltage.
A program in accordance with a second aspect of the present invention causes a computer system to function as each of the units in the above-mentioned vehicular steering device.
That is, a function for realizing each of the units in the above-mentioned vehicular steering device can be provided as a program to be performed by a computer system.
In a computer-readable record medium in accordance with a third aspect of the present invention, a program for causing a computer system to function as each of the units in the above-mentioned vehicular steering device is recorded.
In the case of such a program, the program may be recorded in the computer-readable record medium, for example, a ROM or a backup RAM, and the ROM or the backup RAM may be used in combination with the computer system.
In addition, the above-mentioned program may be recorded in a computer-readable record medium such as a semiconductor memory (smart medium, memory stick, or the like), a hard disk, a floppy disk, a data card (IC card, magnetic card, or the like), an optical disk (CD-ROM, CD-R, CD-RW, DVD, or the like), a magneto-optical disk (MO or the like), a phase-change disk, a magnetic tape, or the like, and that the program be started and used, if necessary, by being loaded into the computer system.